A photon's random walk JUN 27 2013

The center of the Sun is extremely dense, and a photon can only travel a tiny distance before running into another hydrogen nucleus. It gets absorbed by that nucleus and the re-emitted in a random direction. If that direction is back towards the center of the Sun, the photon has lost ground! It will get re-absorbed, and then re-emitted, over and over, trillions of times.

This is from 1997, so that figure might have been revised a bit (anyone have updated numbers?) but still, that's incredible. (via hacker news)